1. Field of the Invention
The present invention relates to voltage amplifiers, and more particularly to voltage amplifiers which have a plurality of semiconductor amplifiers operated in a grounded gate or a grounded base configuration.
2. Description of the Prior Art
In symmetrically constructed semiconductor elements, for example, symmetrically doped transistors or field effect transistors, the outer electrodes receive their significance as emitter and collector or, respectively, as source and drain only by means of application of corresponding operating voltages. If drives such as a semiconductor amplifier element into grounded base or, respectively, grounded gate configuration, then, by reversing the operating voltages, the amplification direction of the semiconductor amplifier element can also be reversed. Because of this, matching problems arise as a rule, on the one hand, from the fact that the respective input resistance of the semiconductor amplifier element is relatively low, but the respective output resistance, on the other hand, is relatively high, and these problems arise particularly when a resistor terminating the semiconductor amplifier on one side must be matched to the relatively low input resistance of the semiconductor amplifier element and, to its relatively high output resistance. The terminating resistance represents the source or the load resistance, depending on the operating direction of the semiconductor amplifier. Other problems include, the power consumption with respect to differing amplification demands, particularly when the semiconductor amplifier is to operate in one amplification direction as an input amplifier for relatively small signal levels and is to operate in the other amplification direction as an output amplifier, i.e. as a power amplifier. Such problems can particularly arise when it is a matter of the first or, respectively, last link of an entire chain of semiconductor amplifier elements which can be reversed in amplification direction, as is known, for example, from the German published application No. 26 46 035.
For matching one and the same resistor for both amplification directions, it is known from the German published application No. 26 46 035, for an alternating voltage circuit having a plurality of semiconductor amplifier elements operated in a grounded base (gate) configuration, whose amplification direction is determined by the application of specific voltages and, therefore, can be reversed by means of changing these voltages, to provide an operating direct voltage feed for the emitter electrode (source) and for the collector electrode (drain) of the individual semiconductor amplifier elements. The operating direct voltage feed is designed mutually reversible. It is also known to iteratively connect the semiconductor amplifier elements in stages upon interposition of a respective four-terminal network having a band pass character which, for both amplification directions, transforms the respective output resistance of one stage into the input resistance of the succeeding stage in terms of operating direction and to thereby employ switchable components in the transforming four-terminal network, whereby, upon reversal of the amplification direction, semiconductor diodes which are likewise to be reversed can be employed for reversing these components.